Michael J. Fox: 'I'm So Blessed'

Diagnosed with Parkinson's 15 years ago, Michael J. Fox hasn't let the ravages of the disease take his attention from what's really important: His wife, kids and quest for a cure.

"I'm so blessed with a great family, and I've had success in my career," the actor, who's been campaigning for candidates who support embryonic stem-cell research, tells PEOPLE in its new issue. "I feel this is a really unique opportunity for me to help out and try to effect change."

Fox, 45, says his condition is now so much a part of his life that even his kids with wife Tracy Pollan – Sam, 17; twins Aquinnah and Schuyler, 11; and Esme, 5 – barely mention it anymore. "They know it so intimately," he says. "It would be like asking your mother what it's like to be that tall."

The disease is also a learning experience for his children. "I think the thing it has taught my kids is resilience," he says. "And that's a great lesson and a great gift I've been able to give them just by example."

Although he first revealed his illness publicly in 1998, he's been in the public eye more than ever recently, in political ads and TV interviews that showcase the involuntary movements often associated with Parkinson's.

"I have less control over the way my body moves," he says. "The thing that gets tougher as you go along is that the medication gets less effective and has more side effects. So it's a lot more challenging."